Collision protection devices for use in motor vehicles of the type having an inflatable air bag which are triggered by a collision detection sensor are well known from the prior art. These air bag devices typically use a collision detection sensor unit which consists of one or more acceleration sensors which measure the acceleration or deceleration of the vehicle in order to send a triggering signal to the inflatable air bag mechanism when an accident of the appropriate severity is taking place. This triggering signal is either used directly to activate one or more pyrotechnic propellant charges to inflate the air bag or it is relayed to a switch which, in turn, ignites the propellant charge. Upon ignition, the pyrotechnic propellant charge fills the air bag within several milliseconds, thus forming an effective protective air cushion for the passenger to protect the driver from impacting his or her body and head against the steering wheel and/or dash board area of the motor vehicle.
During a front end collision, the passengers bodies are moving forward with great momentum and thus the possibility of a sudden body recoil (whiplash) is very great. Therefore, in order to catch the forward moving bodies in a soft and recoil-free manner, it is desirable to provide the air bag with one or more blow-out elements which release the propellant gas in a controlled manner as the passenger strikes the air bag so that is cushions the impact by deflating. These known blow-out elements are typically nothing more than openings in the air bags and, as a consequence, a considerable portion of the propellant gas is permitted to escape from the air bag and come into direct contact with the driver and passengers (if any) in the confines of the vehicle passenger compartment.
The combustion of these propellant gases also produces a lot of smoke (gases and particulates) which are unpleasant to smell and irritate the eyes, nose, and throats of the passengers within the vehicle. The overall air volume of the combustion gases contained in the air bag, as well as, the amount of gas that flows out of the air bag, is very large considering that the average driver side air bag has an air capacity of around 80 liters. And, if separate air bags are provided for the front and rear passengers, there may be as much as an additional 80-250 liters of combustion gases present in the passenger compartment after an accident. In addition to the unpleasant smell and the irritation of the passengers' eyes, throat and nose, breathing the combustion gases for a long period of time poses a health risk. For these reasons, it is desirable to greatly reduce the amount of combustion gases and particulates to which the passengers are exposed and must breathe. Another concern is to reduce passenger/driver anxiety and/or panic, since the smoke and smell of the scorched gaskets associated with detonated propellant charge are symptoms which can be mistaken for a vehicle fire.
These problems have become well known through the evolution pyrotechnic propellant-activated air bags, and there have been many attempts to improve the delivery system of inflatable air bags to overcome the disadvantage of unpleasant smell, poor visibility and irritation to the eyes, nose and throat associated with the exposure to the smoke and combustion gases. For example, German Patent document DE-PS 32 35 176 discloses how to arrange a container filled with aromatics within the inflatable air bag which automatically opens during the course of inflation of the air bag. The aromatic substances, when released, serve to lessen the irritation of the passengers' nose and throat from the combustion gases as they are inhaled. This method does not satisfactorily solve all the above-mentioned problems since the aromatics only adulterate the noxious combustion gases and do not overcome the problems of eye irritation and smoke production nor does it remove the noxious components from the combustion gases, it merely masks them with additional aerosols.
Another method is directed to improving the combustion gases that are released into the passenger compartment. This method is disclosed in DE-PS 36 44 554, wherein a filter is provided to a portion of a wall of an inflatable air bag adjacent the blow-out elements. The filter is designed to prevent the particulates which are released from ignition of the propellant gas from escaping through the blow-out elements of the air bag and seeping into the passenger compartment. The ability of this filter to filter out fine particles (elements) is compromised since the filter must have a relatively large mesh in order to allow the combustion gas to flow rapidly out of the inflating air bag to permit a sufficiently soft (recoil free) deflation-type cushioning surface for the passenger. However, effective removal of all the harmful gases requires that the filter be very tight or thick (i.e., a very fine mesh), but a thick filter hinders the outflow process, and thus impairs the necessary recoil (anti-whiplash) operation of the air bag. In reality, only relatively large particles are prevented from escaping through the air bag filter of this type and these large particles constitute only a minor portion of the total combustion gases. Thus, a major portion of the aforementioned noxious fumes and smoke particulates are still permitted to escape into the passenger compartment when using this method and the health problems and poor visibility conditions still exist.
It is also known from the prior art to provide a device which measures and monitors the oxygen content in the passenger compartment. An example of such a known device is disclosed in JP 59-206215 A, wherein it is disclosed to provide an oxygen sensor to measure the oxygen concentration in the passenger compartment and which also is used to send an alarm signal to activate a fan for ventilation of the passenger compartment when a specified limit value is exceeded. A similar device is disclosed in JP 55-145015 A, wherein the sensor automatically opens or shuts the windows of the passenger compartment depending on the concentration of tobacco smoke which is detected by the sensor. These types of devices call for the use of gas sensors which are expensive and are otherwise undesirable for use in conjunction with air bag devices since they typically have rather long response times and therefore are not well-suited to solve the above mentioned problems associated the combustion gases.
Another problem associated with inflatable air bags is the sudden increase in air pressure experienced within the passenger compartment caused by the sudden passenger compartment volume decrease upon rapid inflation of the air bag. This sudden pressure increase is unpleasant, and in extreme cases, can result in injury to the passenger(s), e.g. rupture of the eardrum(s). Both DE-OS 33 12 769 and DE-AS 21 31 479 disclose a common method for remedying this situation wherein a portion of the window pane of the vehicle is shattered simultaneously with the activation of the pyrotechnic charge so that the resulting pressure wave within the passenger compartment can escape to the outside ambient atmosphere. Since the purpose of creating an opening in the window pane is to equalize the internal passenger compartment pressure with the outside ambient atmosphere, the opening is not required to be very large. Therefore, after pressure equalization has occurred, there is virtually no more exchange of air through the shattered region of the window. Thus, the health and visibility problems and irritation to the passengers' mucous membranes caused by the combustion gases and smoke still exist since the gas escaping from the air bag does not flow fast enough through the shattered region of the window to clear the passenger compartment.
Another problem with motor vehicles equipped with air bag collision protection devices arise in the situation where the driver and/or passengers must exit or be removed from the vehicle quickly due to the potential danger of a vehicle explosion or fire which is made difficult due to the presence of the inflated air bag and the blinding smoke within the passenger compartment. DE-OS 31 16 867 provides a switching circuit which activates the emergency functions in the automobile wherein the collision sensor for use in activation of the inflatable air bag is also used for the simultaneous activation of emergency functions, such as: 1) shutting off the fuel pump; 2) opening a central locking device; and 3) turning on a warning signal flasher system. While such a switching circuit reduces the possibility of a vehicle fire and enables the passengers to see and operate the door mechanisms in order to exit the vehicle more quickly (or be helped by rescue personnel) in order to escape the noxious fumes and smoke of the combustion gases, this switching circuit does not alleviate the above mentioned problems in the situation where no rescue personnel are present and where the passengers are unable to quickly exit the passenger compartment, (i.e., they are unconscious or the doors are damaged and won't open).
Accordingly, there is a great need in the art for a simple and cost effective implementation of an air bag detection device for motor vehicles wherein the noxious combustion gases and fine smoke particulates associated with the detonated pyrotechnic propellant charge are quickly removed from the passenger compartment upon inflation of the air bag.